The present invention relates to a radio positioning system and a coordinate configuring method, and particularly to a radio positioning system and a coordinate configuring method for measuring a position of a radio terminal by using ultra wide band radio technology.
A radio positioning system disclosed in Patent Document 1 uses three or four radio base stations to detect a position of a radio terminal by using time differences of arrival between signals received by the radio terminal.
FIG. 26 is an overall view of a positioning system for detecting a position of a radio terminal as disclosed in Patent Document 1. As shown in FIG. 26, the positioning system 1801 includes radio base stations 1811, 1812 and 1813, and a calculation server 1814. The radio base stations 1811, 1812 and 1813 and the calculation server 1814 are connected to one another through a wire network 1815. The positioning system 1801 uses time differences of signal arrival between measurement signals 1816, 1817 and 1818 transmitted/received between a radio terminal 1810 and the respective radio base stations to measure the position coordinates of the radio terminal 1810. To obtain absolute time of signal arrival of each of the measurement signals 1816, 1817 and 1818, the clock of the radio terminal 1810 needs to be synchronized with the clock of each radio base station.
In the positioning system using general radio communication, the radio terminal is however asynchronous with each radio base station. For this reason, the positioning system using general radio communication cannot perform positioning using absolute time of arrival (TOA). Time differences of arrival (TDOA) of measurement signals from the radio terminal to the respective radio base stations can be however obtained when the clocks of the radio base stations are synchronized. Accordingly, positioning using relative time of arrival (time differences of arrival (TDOA)) can be performed. The positioning system 1801 shown in FIG. 26 uses the latter method to obtain time differences of arrival to thereby measure the position coordinates of the radio terminal 1810.
[Patent Document 1] JP-A-2004-242122 (page 6, page 12, FIG. 1)
In the radio positioning system disclosed in Patent Document 1, it is however necessary to synchronize the clocks of the base stations 1811, 1812 and 1813 because the position of the radio terminal is measured based on time differences of arrival to the base stations 1811, 1812 and 1813. For this reason, it is necessary to connect the base stations to one another by cable or provide a reference station separately from the base stations 1811, 1812 and 1813 for measuring the position coordinates of the radio terminal 1810 in order to synchronize the clocks of the base stations.
To measure the position of the radio terminal 1810 based on time differences of arrival to the base stations 1811, 1812 and 1813, it is necessary to hold relative position relations between the base stations as data in advance. Therefore, the positions (unified coordinates) of the respective base stations must be measured in advance and the position information must be input to the respective base stations.